1. Field of the Invention
This invention relates to storm shutters, and in particular to an automatic storm shutter.
2. Background of the Invention
In the brief interval before a tornado is sighted and it's actual strike, it is unrealistic to expect occupants of structures to close their windows, shutters, etc. All the occupants can be expected to do is to protect themselves as best they can.
In trying to design a building that is capable of surviving tornado-strength winds, it is crucial that the windows, as required by practicality and building codes, be able to protect themselves automatically and instantaneously from high winds, flying debris, and yet be able to provide ventilation when required.
Accordingly, it would be desirable to provide an automatic storm shutter capable of sensing the abrupt decrease in pressure which occurs immediately before a tornado strikes, and to quickly respond by automatically closing the shutter to protect the structure aperture it then covers.
It is extremely important that the automatic storm shutter react very quickly and automatically. By the time high, tornado-force winds arrive, it is too late. These winds can ascend to 300 miles per hour. The severe and sudden pressure drop which occurs immediately before a tornado strikes is virtually the only solid indication of the imminent arrival of a tornado, with potentially disastrous results. This drop in pressure could occur in as little as one to three seconds prior to the tornado striking, so fast reaction and closing on the part of the automatic storm shutter is crucial.
In addition, it would be desirable to provide an automatic storm shutter which affords shade from the sun to the structure opening it protects. This ability can greatly improve the air conditioning efficiency, and reduced the summer cooling load in the structure, when a storm is not present.
Existing Designs
A number of approaches have been attempted to deal with this problem. U.S. Pat. No. 7,342,375 was granted Johansen for an automatic storm shutter control which used an electric motor to close roll-down shutters when commanded by a rain sensor. While this design closed shutters when rain was detected, it's operation was too slow to respond to a tornado, which could require fast, one-second reaction time to close the shutter.
Another problem could be the power supply for the electric motor. If a power failure has occurred, such as happens frequently in the vicinity of tornados, hurricanes, and other wind storms, this design would not operate. If other stored power sources of actuation were used, such as compressed air or stored electricity, the complexity, number of failure modes, and cost of the design would increase.
In addition, no provision was taught to close the shutter as a response to high, tornado-strength winds—only rain. It is possible to be hit by a tornado without rain, so this design would not command the storm shutters to close in this scenario, depriving the structure openings of protection.
U.S. Pat. No. 3,952,452 was granted Hebda for a device which assisted the closing of a door. This invention was intended to be used to assist the opening of a stairwell exit door where a fire-suppressant blower has been actuated to pressurize the air in the stairwell, to prevent fire from spreading floor-to-floor. This pressurization tends to make opening inward-opening doors difficult or even impossible. While this reference taught an apparatus to aid in the opening of such doors using weights and pulleys, no provision was disclosed to rendered the function automatic in the presence of a tornado-induced pressure drop. In addition, this reference taught an aid to open doors, not to close shutters to protect structure apertures.
U.S. Pat. No. 4,750,303 was granted Mullen for a silo door which would open automatically in the presence of internal silo pressure, such as might be generated by a silo explosion. While this reference taught an automatically opening door, it did not disclose an apparatus to automatically and quickly close shutters to protect structure apertures against imminent tornados.